Heretofore, a fuel cell system has been put to practical use, the system including a fuel cell which receives a supplied reactant gas (a fuel gas and an oxidizing gas) to generate a power. Moreover, at present, there is suggested a fuel cell system including a secondary cell such as a storage cell in addition to the fuel cell. The system performs an operation (an intermittent operation) for temporarily stopping the power generation of the fuel cell in case of a low load or the like, and returns to a usual, operation to restart the power generation in case of a load increase or the like (e.g., see Patent Document 1).    Patent Document 1: Japanese Patent Application Laid-Open No. 2003-303605